1. Field of the Invention
The present invention concerns a method of influencing a melt temperature in a plasticizing cylinder of a plasticizing unit.
2. Description of Related Art
In plasticizing units of the general kind set forth, unwanted axial temperature gradients occur in the screw prechamber during plasticization of the melt reservoir required for the injection procedure. The reason for this is a reduction in the effective screw length (see C. Rauwendaal, “Polymer Extrusion” 4th edition, Hanser Munich 2001) in the metering operation and the change linked thereto in the shearing history and the residence time of individual granules and fluid elements as well as the axial temperature gradients in the plasticizing cylinder.
In an injection molding process, the melt temperature in the screw prechamber can be influenced by the following control parameters (see for example DE 10 2010 024 267 A1 and J. L. White, H. Potente, “Screw Extrusion”, Hanser Munich, 2003):
Temperature control in the plasticizing cylinder:                The temperature of the melt is influenced by means of suitable profile presettings with respect to heating of the plasticizing cylinder.        
Dynamic pressure:                The temperature of the melt is influenced by means of suitable profile presettings with respect to dynamic pressure regulation of the plasticizing unit.        
Screw rotary speed (or screw peripheral speed):                The temperature of the melt is influenced by means of suitable profile presettings with respect to rotary speed regulation of a motor of the plasticizing screw of the plasticizing unit.        
The use of temperature control of the plasticizing cylinder as a control parameter for melt temperature regulation can only be implemented in a limited manner when using conventional cylinder heating by means of ceramic heating bands by virtue of inertia of the system and poor temperature conductivity of the melt.
A better intervention option is afforded here by a change in the rotary speed and/or the dynamic pressure, for example, a rising speed or dynamic pressure towards the end of the plasticizing procedure in order on the one hand to ensure a higher input of energy into the melt, and on the other hand to increase the residence time of the melt in the plasticizing screw.